Turtles stomp in the fight. Not sure if they'd figure out how to turn him back, unless just capturing him and calming him down worked.
Connors should take any 1 of the turtles, and any 2 would likely be a good fight. Because, iirc, none of the turtles have class 10 strength and comparable reflexes. But 4's a stomp.
Don, Raph, and Leo were able to beat a mutated crocidile (Leatherhead) in the sewers. Leo also beat a giant Albino croc when he was a toddler using pressure points. Plus they have defeated and captured countless other mutants with Dons monster capturing equipment. If given a day or a couple of hours I'am pretty sure Don can change Connors back. However he needs the necessary equipment. I dont think any of the stuff in their lair is going to do any good so they would probably have to find conors lab.
Its not going to be that easy buts its possible for them to take the Lizard down.